The dim galaxy filled with blue stars was first noticed last year by a different group of researchers, who also used the workhorse telescope to make the previous age estimate. It reigned as the most ancient galaxy observed until last month when it was knocked off its perch by another distant galaxy.

Now it’s back on top after the team used a longer exposure time to get a clearer view of the earliest and far-off galaxies. Seeing the most distant galaxies is like looking back in time and this one existed when the universe was in its infancy — about 380 million years old.

Besides refining the galaxy’s age, they found half a dozen new early ones.

‘‘People have found one object here and there,’’ but never so many early galaxies, said Richard Ellis, an astronomer at the California Institute of Technology who led the new work.

The findings will be published in the Astrophysical Journal Letters.

Scientists are excited about the bounty of early galaxies, which should help refine theories about the formation of the first stars and galaxies. Astronomers think galaxies started appearing after the Big Bang, the explosion believed to have created the universe 13.7 billion years ago. Our Milky Way — one of hundreds of billions of galaxies — formed about 10 billion years ago.

‘‘We want to know our cosmic roots, how things got started and the origins of the galaxies that we see nowadays,’’ said Harvard University astrophysicist Avi Loeb, who had no role in the latest research.

Launched in 1990, Hubble has consistently peered back in time to reveal ancient and distant objects. The farther away something is, the longer it takes for its light to travel to Earth, which scientists use to estimate its age.

As far back as Hubble can see, it still can’t capture the earliest galaxies. That job is left to its more powerful successor, the James Webb Telescope, to be launched in 2018.